The present invention relates in general to the field of organic synthesis, and more particularly to a method for producing organic carbonates.
Alkylene carbonates are valuable compounds that are useful in a variety of applications, either directly, or as reactive intermediates. Examples of such applications include uses as cleaning and stripping agents, monomers for making polycarbonate plastics, alkoxylating agents for use in producing reactive intermediates, incorporation into plant protection agents and pharmaceuticals, and the synthesis of carbamates.
It is known that alkylene oxides will react with carbon dioxide and a suitable catalyst to produce organic carbonates. However, to achieve industrially acceptable reaction rates, high temperatures and pressures are often used. Such conditions are expensive to maintain and often result in decomposition of the carbonate precursors.
Additional problems are encountered when higher molecular weight alkylene oxides are used. The carbonates produced from these alkylene oxides are typically solids at room temperature, and viscous liquids under reactor conditions. The increase in viscosity as the reaction proceeds inhibits effective mixing and carbon dioxide uptake, and thus lowers the yield. The product, containing unreacted starting material, must then be removed from the reactor while very hot to avoid the problems associated with solidification of the product mixture.
There exists a need for a method for the production of carbonates that melt at a high temperature, which process both increases the yield of the product, and facilitates the handling of the product once it is produced.
The present invention solves the problems of reduced yields and difficulty in manipulating higher-melting organic carbonates.
The present invention is a method for the production of organic carbonates by reacting an alkylene oxide and carbon dioxide in the presence of a catalyst and a solvent. The solvent used in the various forms of the present invention can be glyme, diglyme, tetraglyme, cumene, toluene, tetrahydofuran, cyclohexanone, ethylbenzene, aromatic hydrocarbons, or ethers. The catalyst used can be a tetraalkyl ammonium halide, such as tetraethyl ammonium bromide. The alkylene oxide that can be used in the invention can include Bisphenol A, Bisphenol B, Bisphenol F, alkylene oxides that have alkyl substituent groups, alkylene oxides that have aryl substituent groups, and alkylene oxides that contain both alkyl and aryl substituent groups.
An advantage of the present invention is that the claimed method results in near quantitative (that is, almost 100%) conversion of starting materials into carbonate product. Additionally, the presence of the essentially pure carbonate in a solvent matrix facilitates the collection and distribution of the material for further use. An essentially solvent-free carbonate can be prepared by flash removal of the solvent.
The compositions of the present invention contain a wide variety of other organic solvents. Non-limiting examples of representative classes of such solvents include hydrocarbons, ethers, esters, sulfur-based solvents, chlorinated hydrocarbons, aromatic hydrocarbons nitrated hydrocarbons, amides, and ketones. Such solvents may be polar or non-polar, may be protic or aprotic, may be cyclic, branched, or straight chain, and may contain one or more functional groups.
While a wide variety of organic solvents can be used in the compositions of the present invention, some solvents that might be predicted to work do not. For example, propylene carbonate produces low yields of carbonates under the same conditions that lead to quantitative conversion using other solvents.
Representative examples of common hydrocarbon solvents appropriate for use in the present invention include, but are not limited to, toluene, xylene, and mixtures of aromatic hydrocarbons.
Examples of common ether solvents that may be used in the present invention include, but are not limited to, tetrahydrofuran, dioxane, glyme, diglyme, tetraglyme, dibutyl ether, and diphenyl ether.
Examples of common sulfur-based solvents that can be used in the present invention include, but are not limited to, dimethylsulfoxide (DMSO) and sulfolane.
Representative examples of common chlorinated hydrocarbon solvents include, but are not limited to, methylene chloride, methyl chloroform, chlorobenzenes and dichlorobenzenes.
Representative examples of common amide solvents include, but are not limited to, formamide, dimethyl formamide, acetamide, and dimethylacetamide.
Representative examples of common ketone solvents include, but are not limited to, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, methyl isoamylketone, and cyclohexanone.